Validation of Operational pre/potential Tropical Cyclones (pTCs) Using Model Diagnostics

This study uses diagnostics of the Global Forecast System (GFS) and European Centre for Medium-Range Weather Forecasting (ECMWF) models to validate pre or potential Tropical Cyclone (TC) operational tracks. Disturbances that precede tropical cyclones are tracked using satellite imagery and model fields by the National Hurricane Center (NHC) and the Joint Typhoon Warning Center (JTWC) and are designated as “Invests” or “9X” storms. The TC “diagnostics files” used as input into the dynamical-statistical SHIPS and LGEM intensity forecast models provide statistics for spatially averaged large-scale, environment variables surrounding the pTC as it is tracked by NHC/JTWC. Disturbances from 2007-2015 are studied as they either develop into a tropical cyclone, or dissipate (i.e., non-developers). This study discusses differences in variables between the pTCs that develop and those that never reach the TC stage. We find substantial differences in variable trends over time between developing and non-developing pTCs. Those that develop show lower shear, higher precipitable water, higher relative humidity, and more tendencies toward warm core systems as much as 2-4 days before development. These differences are consistent across all global basins and several years. Furthermore, two case studies are discussed -- one in early summer 2015 and the other in January 2014 (a 10-d ‘landphoon' over western Australia) that demonstrate the value of operational pTCs and that provide insight into TC genesis.